This is a case-control study involving 230 patients and 230 "best friend" controls designed to elucidate risk factors in the development of primary glial tumors of the brain. The control who is provided by the patient, is a person of the same sex, within 5 years of age, living within 100 miles and not a blood relative. Both patients and controls are given a 45 page questionnaire to complete. Telephone followups are performed to further clarify responses. Areas covered by the questionnaire include family history, medical background, environmental and occupational exposures.